-
[show abstract]
[hide abstract]
ABSTRACT: The aims of this study were twofold: first, to determine the impact of variance in dose-volume histograms (DVH) on patient-specific toxicity after 2 high-dose fractions in a sample of 22 men with prostate cancer; and second, to compare the effectiveness of traditional DVH analysis and principal component analysis (PCA) in predicting rectum and urethra toxicity. A series of 22 patients diagnosed with prostate adenocarcinoma was treated with 45 Gy external beam and 20 Gy dose rate brachytherapy. Principal component analysis was applied to model the shapes of the rectum and urethra dose-volume histograms. We used logistic regression to measure the correlations between the principal components and the incidence of rectal bleeding and urethra stricture. We also calculated the equivalent uniform dose (EUD) and normal tissue complication probability (NTCP) for the urethra and rectum, and tumor control probability (TCP) for the prostate using BioSuite software. We evaluated their correlations with rectal and urethra toxicity. The rectum DVHs are well described by one principal component (PC1), which accounts for 93.5% of the variance in their shapes. The urethra DVHs are described by two principal components, PC1 and PC2, which account for 94.98% and 3.15% of the variance, respectively. Multivariate exact logistic regression suggests that urethra PC2 is a good predictor of stricture, with Nagelkerke's R2 estimated at 0.798 and a Wald criterion of 5.421 (p < 0.021). The average NTCPs were 0.06% ± 0.04% and 1.25% ± 0.22% for the rectum and urethra, respectively. The average TCP was 85.29% ± 2.28%. This study suggests that principal component analysis can be used to identify the shape variation in dose-volume histograms, and that the principal components can be correlated with the toxicity of a treatment plan based on multivariate analysis. The principal components are also correlated with traditional dosimetric parameters.
Journal of Applied Clinical Medical Physics 01/2013; 14(1):3882. · 1.29 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The aim of this study was to compare lumpectomy cavity depth measurements obtained through ultrasound (U/S) and retrospective computed tomography (CT). Twenty-five patients with stage T1-2 invasive breast cancer formed the cohort of this study. Their U/S and CT measurements were converted into electron energy and compared. The mean U/S depth was 3.6 ± 1.3 cm, while the mean CT depth was 4.9 ± 1.9 cm; the listed error ranges are one standard deviation. Electron energies for treatment ranged from 6 MeV to 12 MeV based on the U/S determination. There was no significant correlation between cavity depths measured by U/S and CT (R(2)= 0.459, P < 0.002). Furthermore, only 20% of CT-based electron energy determinations matched the corresponding U/S determinations. This ratio increased to 40% when taking into account an upper limit based on the depth of organs at risk below the cavity. The study shows that there is a significant discrepancy between cavity depths determined by U/S and CT. It also supports the concept that post-lumpectomy radiotherapy boosts should be tailored according to the needs and comfort of individual practices and institutions.
Journal of Medical Physics 07/2012; 37(3):138-44.
-
[show abstract]
[hide abstract]
ABSTRACT: To assess dosimetric parameters in a case study where bilateral accelerated partial breast irradiation (APBI) is delivered using a strut-adjusted volume implant (SAVI) device. A 59-year-old female received APBI in both breasts over 5 days, with fractions of 3.4 Gy twice daily. A Vac-lok system was used for immobilization, and a C-arm was used for daily imaging. We generated dose-volume histograms (DVHs) for the brachytherapy plans to derive several important biologic factors. We calculated the normal tissue complication probability (NTCP), equivalent uniform dose (EUD), and tumor control probability (TCP) using the Lyman-Kutcher-Burman model parameters α = 0.3 Gy(-1), α/β = 4 Gy, n = 0.1, and m = 0.3. In addition, we assessed the dose homogeneity index (DHI), overdose index, and dose nonuniformity ratio. D95 was >95% and V150 was <50 mL for both breasts. The DHIs were 0.469 and 0.512 for the left and right breasts, respectively. The EUDs (normalized to 3.4 Gy b.i.d.) were 33.53 and 29.10 Gy. The TCPs were estimated at 99.2% and 99.9%, whereas the NTCP values were 4.2% and 2.57%. In this clinical case, we were able to quantify the dosimetric parameters of an APBI treatment performed with a SAVI device.
Medical dosimetry: official journal of the American Association of Medical Dosimetrists 12/2011; 37(2):214-20. · 1.26 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The objective of this work is to evaluate biological models and dose homogeneity in a new partial breast irradiation method, the MammoSite RTS. The study is based on 11 patients who received the therapy. For each patient, we determined the dose volume distribution delivered to the breast. Based on these data, we estimate some important biological parameters. Eleven patients with early-stage, invasive, ductal breast cancer were treated using MammoSite RTS brachytherapy, which delivers radiation through a balloon placed in the lumpectomy bed. The radiation was provided by an Iridium-192 source, and 340 cGy were delivered per fraction twice daily. We calculated some commonly used dosimetric parameters, and evaluated the biological parameters tumor control probability (TCP) and normal tissue complication probability (NTCP). We also looked for correlations among these parameters. The average equivalent uniform dose (EUD), NTCP, and TCP were 43.66 Gy, 47.95%, and 91.78%, respectively. The coefficient of variation (CV) among the patients was very low for all 3 parameters. Two dose homogeneity indices (DHI and the S-index) are strongly correlated (r = -0.815). The area under the dose-volume histogram (DVH) and the treatment volume (TXV) also showed a strong correlation (r = 0.995, p < 0.0001). A simplified logit Poisson-EUD model is suitable for determining NTCP and TCP. Other factors such as the area under the DVH and dose homogeneity indices are also useful in planning radiotherapy treatments for early breast cancer.
Medical dosimetry: official journal of the American Association of Medical Dosimetrists 01/2009; 34(3):207-13. · 1.26 Impact Factor
